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U631H64DC45G1 Datasheet(PDF) 10 Page - Simtek Corporation |
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U631H64DC45G1 Datasheet(HTML) 10 Page - Simtek Corporation |
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10 / 13 page  U631H64 10 March 31, 2006 STK Control #ML0045 Rev 1.0 Device Operation The U631H64 has two separate modes of operation: SRAM mode and nonvolatile mode. In SRAM mode, the memory operates as a standard fast static RAM. In nonvolatile mode, data is transferred from SRAM to EEPROM (the STORE operation) or from EEPROM to SRAM (the RECALL operation). In this mode SRAM functions are disabled. SRAM READ The U631H64 performs a READ cycle whenever E and G are LOW while W is HIGH. The address specified on pins A0 - A12 determines which of the 8192 data bytes will be accessed. When the READ is initiated by an address transition, the outputs will be valid after a delay of tcR. If the READ is initiated by E or G, the outputs will be valid at ta(E) or at ta(G), whichever is later. The data outputs will repeatedly respond to address changes within the tcR access time without the need for transition on any control input pins, and will remain valid until another address change or until E or G is brought HIGH or W is brought LOW. SRAM WRITE A WRITE cycle is performed whenever E and W are LOW. The address inputs must be stable prior to entering the WRITE cycle and must remain stable until either E or W goes HIGH at the end of the cycle. The data on pins DQ0 - 7 will be written into the memory if it is valid tsu(D) before the end of a W controlled WRITE or tsu(D) before the end of an E controlled WRITE. It is recommended that G is kept HIGH during the en- tire WRITE cycle to avoid data bus contention on the common I/O lines. If G is left LOW, internal circuitry will turn off the output buffers tdis(W) after W goes LOW. Noise Consideration The U631H64 is a high speed memory and therefore it must have a high frequency bypass capacitor of appro- ximately 0.1 μF connected between V CC and VSS using leads and traces that are as short as possible. As with all high speed CMOS ICs, normal carefull routing of power, ground and signals will help prevent noise problems. Software Nonvolatile STORE The U631H64 software controlled STORE cycle is initiated by executing sequential READ cycles from six specific address locations. By relying on READ cycles only, the U631H64 implements nonvolatile operation while remaining compatible with standard 8K x 8 SRAMs. During the STORE cycle, an erase of the pre- vious nonvolatile data is first performed, followed by parallel programming of all nonvolatile elements. Once a STORE cycle is initiated, further inputs and outputs are disabled until the cycle is completed. Because a sequence of addresses is used for STORE initiation, it is important that no other READ or WRITE accesses intervene in the sequence or the sequence will be aborted and no STORE or RECALL will take place. To initiate the STORE cycle the following READ sequence must be performed: 1. Read address 0000 (hex) Valid READ 2. Read address 1555 (hex) Valid READ 3. Read address 0AAA (hex) Valid READ 4. Read address 1FFF (hex) Valid READ 5. Read address 10F0 (hex) Valid READ 6. Read address 0F0F (hex) Initiate STORE Once the sixth address in the sequence has been entered, the STORE cycle will commence and the chip will be disabled. It is important that READ cycles and not WRITE cycles are used in the sequence. It is not necessary that G is LOW for the sequence to be valid. After the tSTORE cycle time has been fulfilled, the SRAM will again be activated for READ and WRITE operation. Software Nonvolatile RECALL A RECALL cycle of the EEPROM data into the SRAM is initiated with a sequence of READ operations in a manner similar to the STORE initiation. To initiate the RECALL cycle the following sequence of READ opera- tions must be performed: 1. Read address 0000 (hex) Valid READ 2. Read address 1555 (hex) Valid READ 3. Read address 0AAA (hex) Valid READ 4. Read address 1FFF (hex) Valid READ 5. Read address 10F0 (hex) Valid READ 6. Read address 0F0E (hex) Initiate RECALL Internally, RECALL is a two step procedure. First, the SRAM data is cleared and second, the nonvolatile information is transferred into the SRAM cells. The RECALL operation in no way alters the data in the EEPROM cells. The nonvolatile data can be recalled an unlimited number of times. Automatic Power Up RECALL On power up, once VCC exceeds the sense voltage of VSWITCH, a RECALL cycle is automatically initiated. The voltage on the VCC pin must not drop below VSWITCH once it has risen above it in order for the RECALL to operate properly. |
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